The present invention relates generally to the field of metal peening, and more particularly, to methods and devices for ultrasonic peening of metals for general strengthening and stress relaxation of metals.
Ultrasonic peening of metals has been known for many years. For example, SU Patent 472,782 discloses a device for treatment of metals with an ultrasonic oscillation using a magnetostrictive transducer. The device comprises a transducer, an ultrasonic velocity transformer and a holder in the form of guide skirt with holes in its bottom connected in series. Tools in the form of stepped rods are located in the holes. The holder is attached to a flange located in a nodal plane of the ultrasonic velocity transformer, and the rods are axially displaceable in a direction perpendicular to a surface to be treated. The main disadvantages of this device are:
the holder is fixedly fastened in the nodal plane of the ultrasonic velocity transformer resulting in non-uniform treatment of metal surfaces by multiple-striker heads;
the rod tools usually function under heavy conditions of high-frequency impact loading, are subject to wear and fatigue destruction, and their replacement is time consuming causing reduced efficiency of treatment;
the use of magnetostrictive transducers for ultrasonic peening also has its disadvantages, since the transducers of this kind often require pumped cooling water systems which makes such devices more complicated, heavier and increases the cost of the equipment; and
the stepped rods or pins have thickenings at their upper ends to keep them in the working head during treatment which significantly complicates the process of their manufacture and reduces their service life.
The above mentioned disadvantages are to some extent reduced in an ultrasonic device for strengthening of metal surfaces disclosed in Ukrainian Patent No. 13,936 dated January 1997. This teaches a device which has connected in series, a transducer, an ultrasonic velocity transformer and a holder in the form of guide skirt with holes in its bottom. Pins with conical thickenings are located in the holes, and the holder is mounted for free rotation. The holder is retained on the body of the device by a cylindrical ring spring which fits in an appropriate groove of the ultrasonic velocity transformer. A plate made of a high-strength material is located between the pins and the end of the ultrasonic velocity transformer. The disadvantages of this ultrasonic device are:
when operating for a period exceeding 3-5 minutes the tool and the holder are, as a result of impact energy absorption, heated up to the temperature more than 100xc2x0 C., and after this it is necessary to interrupt treatment to cool the head; and
the working head has striking tools arranged in a honeycomb pattern, which is intended mainly for strengthening of flat surfaces. This pattern of tools is of little use in treating welds having various geometric configurations.
In both of these prior art devices there is a need, because of the inefficiencies of design which result in waste heat being produced for forced cooling. The forced cooling takes the form of stopping the treatment, for example to dunk the working head in water or in oil until it cools down.
It is therefore an object of the present invention to provide a new and improved device for ultrasonic peening of metals, which is easy to use, lightweight, efficient and effective.
It is a further object of the present invention to provide a tool that, on the one hand has an enough power to achieve good peening results and yet on the other hand is small, light weight and can easily be applied by a person to a metal which could benefit from the treatment.
It is a further object of the present invention to provide a new and improved device for ultrasonic peening of metals in which, the ultrasonic generator and piezoelectric transducer operate over a range of powers to optimize the efficient conversion of electric power into ultrasonic power, while simultaneously decreasing the weight of the ultrasonic generator and the transducer, eliminating the necessity of forced cooling of transducer thereof and thus reducing the total cost and weight of the ultrasonic peening equipment.
It is a still further object of the present invention to provide an efficient device for ultrasonic peening of metals that allows for continual passive cooling of the working head, where the amount of cooling increases with increased need of cooling to permit uninterrupted treatment of a workpiece. It is a further object to configure the operative components to provide such continued passive cooling.
It is another object of the present invention to provide a new and improved device for ultrasonic peening of metals which provides multiple replaceable tool heads having a selection of tool configurations such as single-striker, single-row and multiple-striker heads with various diameter of strikers suited to various sizes and types of welds and metal shapes to be treated. It is a further object to configure the operative components of the working head to increase the efficiency of treatment and to increase the service life of device.
Accordingly, the present invention provides a device for ultrasonic peening of metals comprising, connected in series, an power-optimized (most preferably in 0.2 to 0.5 kW range) ultrasonic generator and piezoelectric transducer, an ultrasonic velocity transformer, a holder in the form of a skirt mounted for free rotation around the axis of the ultrasonic velocity transformer, the skirt having holes in its bottom in which pins are located, a plate of a high-strength material located between the pins and the end of the ultrasonic velocity transformer which is fixed to the free end of the transformer for increasing the efficiency of the energy transfer, a casing arranged in a node of an oscillation and filled with a porous material impregnated with a lubricant-coolant, the porous material being foamed polyurethane and said lubricant-coolant being an oil-in-water emulsion with added surfactants, a cylindrical projection located in the lower part of the casing at the middle part of the thin end of the ultrasonic velocity transformer, and a set of replaceable heads adapted for various number, sizes and arrangement of the tools.